import com.sun.xml.internal.ws.api.model.wsdl.WSDLOutput;

import java.util.Scanner;

/**
 * Created with Intellij IDEA.
 * Description;
 * User:TQ02
 * Data:2023-11-10
 * Time:14:46
 * Text：
 */
public class text5 {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int W=sc.nextInt();
        int H=sc.nextInt();
        int n=sc.nextInt();
        int R=sc.nextInt();
        int count=0;
        int[][] array=new int[n][2];
        for(int i=0;i<n;i++){
            int col=sc.nextInt();
            int wol=sc.nextInt();
            array[i][0]=col;
            array[i][1]=wol;
        }
        for(int i=0;i<=W;i++){
            for(int k=0;k<=H;k++){
                for(int m=0;m<n;m++){
                    if((i-array[m][0])*(i-array[m][0])+
                            (k-array[m][1])*(k-array[m][1])<=R*R){
                        count++;
                        break;
                    }
                }
            }
        }
        System.out.println(count);
    }
}
